Writing instrument barrel



FIG. 1 is a front elevational view of a writing instrument barrel showing our new design;

FIG. 2 is a right side elevational view, the left side being a mirror image thereof;

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a left side perspective view thereof; and

FIG. 6 is a rear elevational view thereof. 

The ornamental design for a writing instrument barrel, as shown and described. 